1. Field of the Invention
The present invention relates to a frequency voltage converter, and particularly to a frequency voltage converter capable of holding linearity with respect to a modulated wave signal in a wide frequency band.
2. Description of the Prior Art
FIG. 9 is a circuit diagram showing a configuration of a conventional frequency voltage converter employed in a demodulator circuit as to frequency modulating methods such as FM, FSK, GFSK, etc. In FIG. 9, reference numeral 101 indicates a mixer circuit for converting a modulated wave signal Vin having an intermediate frequency to a frequency voltage, reference numeral 102 indicates a first input terminal of the mixer circuit 101, reference numeral 103 indicates a second input terminal of the mixer circuit 102, reference numeral 104 indicates a first capacitor (capacitance C1) connected to a signal line which branches off toward the second input terminal 103, reference numeral 105 indicates a voltage source, reference numeral 106 indicates a second capacitor (capacitance C2), reference numeral 107 indicates an inductor (inductance L), and reference numeral 108 indicates a resistor (resistance value R), respectively. Further, Vout indicates a signal outputted from the mixer circuit 101.
The operation of the frequency voltage converter will be next described.
When the modulated wave signal Vin is inputted, the relationship between a DC output obtained by removing the harmonics of the output signal Vout, and the modulated wave signal Vin is represented by the following equation (1):
Vin(S)/Vout(S)xe2x88x9ds2LC2/s2L(C1+C2)+sL/R+1,(s=jxcfx89)xe2x80x83xe2x80x83(1)
When the variables in equation (1) are defined as in the following equation (2), the equation (1) is converted to the following equation (3).
xcfx890=1/{square root over (L(C1+C2))},Q=R/xcfx890Lxe2x80x83xe2x80x83(2)
Vout/Vinxcex1xcfx80/2xe2x88x92tanxe2x88x921[Q(xcfx89/xcfx890xe2x88x92xcfx890/xcfx89)]xe2x80x83xe2x80x83(3)
xcfx89xe2x88x92xcfx890 less than  less than xcfx890/Qxe2x80x83xe2x80x83(4)
As is derived from the above equation (3), the voltage of the output signal Vout results in one given as the function of a frequency xcfx89. Under the condition in equation (4) above, the relationship between a DC output of the output signal Vout and the frequency of the input signal Vin approaches a proportionality relation. The center frequency of the input signal Vin is matched with xcfx890 to thereby effect frequency voltage conversion on the input signal Vin.
The conventional frequency voltage converter is accompanied by a problem that since it is configured as described above, a Q value unavoidably results in a large value to maintain input amplitude at the second input terminal 103 where the center frequency xcfx890 is low with respect to a frequency deviation (xcfx89xe2x88x92xcfx890), and hence the value of (xcfx890/Q) becomes small, thereby incurring a difficult execution of frequency voltage conversion with holding linearity with respect to the frequency of the input signal Vin.
The present invention has been made to solve the above-described drawback. It is therefor an object to provide a frequency voltage converter capable of holding linearity with respect to the frequency of an input signal over a wide frequency band and thereby carrying out frequency voltage conversion.
According to a first aspect of the present invention, there is provided a frequency voltage converter comprising: a first transmission line comprised of one signal line which branches off from a signal line for transmitting an input signal corresponding to a modulated wave signal; a second transmission line comprised of the other signal line which branches off from the input signal transmitting signal line; a mixer circuit having a first input terminal connected to the first transmission line and a second input terminal connected to the second transmission line; a delay-amount variable first delay line circuit placed in the second transmission line between a portion where the first transmission line and the second transmission line branch off from each other and the second input terminal of the mixer circuit; a third transmission line comprised of one signal line which branches off from a signal line for transmitting a reference signal having a predetermined frequency; a fourth transmission line comprised of the other signal line which branches off from the reference signal transmitting signal line; a delay-amount variable second delay line circuit placed in the fourth transmission line between a portion where the third transmission line and the fourth transmission line branch off from each other and a portion where the third transmission line and the fourth transmission line are joined to each other; and delay amount control means connected to the third transmission line, the fourth transmission line, a control section of the first delay line circuit and a control section of the second delay line circuit and for outputting the same control signal to the control section of the second delay line circuit and the control section of the first delay line circuit so that the reference signal passing through the fourth transmission line is delayed by a predetermined cycle with respect to the reference signal passing through the third transmission line.
Here, the first delay line circuit may comprise a plurality of stages of unit delay circuits, the second delay line circuit comprises a plurality of stages of unit delay circuits, and the unit delay circuits constituting the first delay line circuit and the unit delay circuits constituting the second delay line circuit respectively have the same circuit configuration.
In addition, when the number of stage of the unit delay circuits series-connected in the first delay line circuit, the number of stage of the unit delay circuits series-connected in the second delay line circuit, the center frequency of the input signal, and the frequency of the reference signal are respectively defined as a, b, fc and fr, the numbers of stage for the first delay line circuit and the second delay line circuit may be respectively set so that a/b=fr/4fc is established, and the frequency of the reference signal may also be adjusted.
On the other hand, when the number of stages of the unit delay circuits series-connected in the first delay line circuit, the number of stages of the unit delay circuits series-connected in the second delay line circuit, the center frequency of the input signal, and the frequency of the reference signal are respectively defined as a, b, fc and fr, the numbers of the stages for the first delay line circuit and the second delay line circuit may be respectively set so that a/b=fr/2fc is established, and the frequency of the reference signal may also be adjusted.
Further, the frequency voltage converter may include: a first buffer and a second buffer disposed in order from the side close to the branch portion between the branch portion and the first input terminal of the mixer circuit in the first transmission line, a third buffer disposed between the branch portion and the first delay line circuit in the second transmission line, a fourth buffer disposed between the first delay line circuit and the second input terminal of the mixer circuit in the second transmission line, a fifth buffer and a sixth buffer disposed in order from the side close to the branch portion between the branch portion and the joined portion in the third transmission line, a seventh buffer disposed between the branch portion and the second delay line circuit in the fourth transmission line, and an eighth buffer disposed between the second delay line circuit and the joined portion in the fourth transmission line, wherein the first buffer, the third buffer, the fifth buffer and the seventh buffer respectively have the same circuit configuration as an output buffer of the each unit delay circuit, and the second buffer, the fourth buffer, the sixth buffer and the eighth buffer respectively have the same circuit configuration as an input buffer of the each unit delay circuit.
According to a second aspect of the present invention, there is provided a frequency voltage converter comprising: a first transmission line comprised of one signal line which branches off from a signal line for transmitting an input signal corresponding to a modulated wave signal; a second transmission line comprised of the other signal line which branches off from the input signal transmitting signal line; a mixer circuit having a first input terminal connected to the first transmission line and a second input terminal connected to the second transmission line; a delay-amount variable delay line circuit placed in the second transmission line between a portion where the first transmission line and the second transmission line branch off from each other and the second input terminal of the mixer circuit; a signal line for transmitting a reference signal having a predetermined frequency; a ring oscillator capable of varying an oscillation frequency; and delay amount control means connected to the signal line for transmitting the reference signal, a signal line for transmitting a signal outputted from the ring oscillator, and a control section of the delay line circuit and a control section of the ring oscillator and for outputting the same control signal to the control section of the ring oscillator and the control section of the delay line circuit so that the frequency of the signal outputted from the ring oscillator coincides with that of the reference signal, wherein the delay line circuit comprises a plurality of stages of unit delay circuits, the ring oscillator comprises a plurality of stages of unit delay circuits disposed in ring form, and the unit delay circuits constituting the delay line circuit and the unit delay circuits constituting the ring oscillator respectively have the same circuit configuration.
According to a third aspect of the present invention, there is provided a frequency voltage converter comprising: a first transmission line comprised of one signal line which branches off from a signal line for transmitting an input signal corresponding to a modulated wave signal; a second transmission line comprised of the other signal line which branches off from the input signal transmitting signal line; a mixer circuit having a first input terminal connected to the first transmission line and a second input terminal connected to the second transmission line; a delay-amount variable delay line circuit placed in the second transmission line between a portion where the first transmission line and the second transmission line branch off from each other and the second input terminal of the mixer circuit; a signal line for transmitting a reference signal having a predetermined frequency; a ring oscillator capable of varying an oscillation frequency; a divider for inputting a signal outputted from the ring oscillator; and delay amount control means connected to the signal line for transmitting the reference signal, a signal line for transmitting a signal outputted from the divider, and a control section of the delay line circuit and a control section of the ring oscillator and for outputting the same control signal to the control section of the ring oscillator and the control section of the delay line circuit so that the frequency of the signal outputted from the divider coincides with that of the reference signal, wherein the delay line circuit comprises a plurality of stages of unit delay circuits, the ring oscillator comprises a plurality of stages of unit delay circuits disposed in ring form, and the unit delay circuits constituting the delay line circuit and the unit delay circuits constituting the ring oscillator respectively have the same circuit configuration.
Here, each of delay-amount variable delay element circuits which are connected and provided by a predetermined number within the each unit delay circuit so as to constitute the unit delay circuit, may be a differential circuit provided with current amount control means and output amplitude control means.
Alternatively, each of delay-amount variable delay element circuits which are connected and provided by a predetermined number within the each unit delay circuit so as to constitute the unit delay circuit, may be configured so that amount-of-current control means are connected in series with CMOS inverter circuits.
Further, a phase detector having a first input terminal connected to the first transmission line and a second input terminal connected to the second transmission line may be disposed in place of the mixer circuit.
Furthermore, the phase detector may be a phase detecting circuit for detecting only delayed phase.